An inline electron gun is one designed to generate or initiate preferably three electron beams in a common plane and direct those beams along convergent paths in that path to a point or small area of convergence near the tube screen. In one type of inline electron gun, such as that shown in U.S. Pat. No. 3,873,879, issued to R. H. Hughes on Mar. 25, 1975, the main electrostatic focusing lenses for focusing the electron beams are formed between two electrodes referred to as the first and second accelerating and focusing electrodes. These electrodes include two cup-shaped members having the bottoms of the members facing each other. Three apertures are included in each cup bottom to permit passage of three electron beams and to form three separate main focus lenses, one for each electron beam. In such electron guns, static convergence of the outer beams with respect to the center beam is usually attained by offsetting the outer apertures in the second focusing electrode with respect to the outer apertures in the first focusing electrode.
It has been noted that the horizontal beam landing locations of the outer electron beams, in color picture tubes having the above-described electron gun, change with changes in the focus voltage applied to the electron gun. It therefore is desirable to improve such inline electron guns to eliminate or at least reduce this sensitivity to focus voltage changes.